The olive tree is considered a robust plant that originally comes from the mild Mediterranean regions. The sometimes harsh Central European climate can cause problems for the tree and make it more susceptible to pests and diseases. Especially when it is wet and cold in winter and rainy in summer, the resistance of the olive tree decreases. As an experienced hobby gardener, you can defy the odds and protect your olive tree from damage.
The most common diseases of an olive tree:
Like pests, diseases are among the greatest threats to the olive tree. There are typical diseases that can occur under unfavorable conditions. If the tree is infested, you must intervene as soon as possible. There are the following diseases:
- olive crab
- eyespot disease
- fire bacterium
- yellowed leaves
Olive crab:
Olive canker, botanically known as Pseudomonas syringae, is a bacterium that settles in the smallest wounds and then nests in the tissue. Growths develop that are similar to cancerous growths in humans.
However, the first signs of the disease can be seen before the growths develop:
- the trunk of the olive tree shows dark red to black lesions that sag and sag in the middle
- the branch bark turns brownish, in the late stage the discolouration tears lengthwise
- thinner, weak branches die off completely, strong branches no longer grow.
- the cell proliferation shifts to the outside, ulcers become visible
There are no classic anti-cancer drugs, neither chemical nor ecological products. If the tree is infested, you as a gardener must take action yourself or take preventive action. The following measures can help:
- Affected plant parts must be generously removed and then burned
- cuts on the olive tree should only be made in advance with disinfected cutting tools
- the olive tree should always be protected from the effects of rain
- Pruning must be done in the spring as there is less risk of injury at this time
- Frost damage such as cracks must be treated with wound protection in winter
Eye spot disease:
The eye spot disease is a fungal infection that is also feared in the large olive plantations of the Mediterranean. The disease can be identified by some classic symptoms:
- affected leaves have brown spots surrounded by a light border
- in the late stage the leaf turns completely yellow and eventually dies
- if the summer is humid and warm, the risk of infection increases
The control of eye spot disease is possible with suitable fungicides as well as with care measures. The recommended course of action depends on the extent of the infestation. - the most important step is the removal of all affected leaves, which should then be burned
- Leaves that have fallen nearby must also be removed
- if the infection has already reached the treetop, a fungicide must be used
The fire bacterium:
One of the most dangerous diseases of the olive tree is the fire bacterium. The harmful effects are so great that the European Commission has already intervened when large-scale cultivation areas were affected. If an olive tree is infested with Xylella fastidiosa, you must also destroy all olive trees within a radius of 100 meters.
There is no cure for the fire bacterium, it can be recognized by these symptoms:
- Fire bacteria establish themselves directly in the xylem of an olive tree
- the pathways that are responsible for the supply of nutrients are misplaced and clogged in this way
- there is no longer any supply of nutrients and water
- all shoots, leaves and flowers first yellow, then wither and die
At first, affected olive trees look like they are under drought stress. Unfortunately, the first symptoms only appear when the infection was several weeks or months ago. Insects are the cause, and meadowfoam planthoppers are particularly common triggers. Not only olive trees, but also peach and lemon trees and oleander bushes can be affected.
leaf yellowing:
Olive trees are relatively lime tolerant, but they cannot handle a massive excess. The result is extensive leaf yellowing, which is not caused by a disease.
If the lime content already reaches alkaline levels, the absorption of magnesium and iron is blocked. The result is leaf yellowing, which is relatively easy to diagnose:
- Areas of the leaves turn yellow, starting at the tip
- Veins of the leaves remain green, creating a typical mosaic pattern
- Foliage turns brown and is shed
The deficiency can be compensated for in the short term by using an iron chelate fertilizer. In the long term, the deficit must be compensated by paying attention to a suitable substrate. The pH should be between seven and eight.
Pests on the olive tree:
Diseases are not the only problem of the olive tree, pests also play a major role. These include, above all, lice in various subspecies. But other troublemakers can also limit the health of the olive tree:
- lice
- mealybugs
- Mealybug
- aphids
- scale insects
- vine weevil
- meadowfoam cicada
Lice and their subspecies:
Above all, there are different types of lice that cause problems for the olive tree. The small pests have extremely sharp mouthparts with which they permanently damage the leaf tissue. The tree is in danger of dying if left unchecked. Different lice have different effects.
The aphid:
Aphids eat through the foliage of the olive tree and leave their honeydew on the leaf. Basically, they are not pests, but beneficial insects, since their dew feeds other animals. Aphids only damage the olive if it is a decrepit tree that no longer has sufficient defenses.
The aphid can be eliminated by consistently showering the tree, the use of chemicals is not necessary.
The mealybug:
Mealybugs, also known as mealybugs, are also actually beneficial because they produce honeydew and thereby feed other insects. If the olive tree is infested with mealybugs, a classic picture emerges.
The insects leave behind wool-like webs. A white covering that is a bit reminiscent of dust flakes under the bed is always an important indication of an infestation with mealybugs.
scale insects:
The really unpleasant plagues include scale insects, which can hardly be treated with contact poisons. A female scale insect lays up to 2000 eggs per year, so the risk of spread is high.
At first, most gardeners don't notice when olive trees are infested with scale insects. The hard shell protects the insects from external influences, they suck the sap from the tree and progressively weaken it. The following symptoms indicate the infestation:
- curled leaves
- dropped leaves
- white coating on the leaves
- brown discoloration of the leaves
- leaves dry up
Treatment of scale insect infestation
In most cases, chemicals are the only remedy for scale insects, as these pests are very stubborn. There are so-called lice sticks that are inserted directly into the substrate. The poison contained in it is transferred to the plant sap without damaging the olive tree itself. The insects, however, absorb the sap and die.
Particularly vulnerable in winter quarters
The olive tree is no friend of the harsh European winter. Olive trees are not used to winter rest, so they become weaker and more susceptible to disease.
If mealybugs or their eggs are sighted during the winter break, you should first reduce them with a brush and a powerful shower. Waxy mealybugs can be removed with a cotton swab soaked in alcohol.
If the symptoms are severe, it may also be necessary to spray with oil, as the treatment suffocates the pests. Another natural treatment method is the use of Australian ladybugs.
vine weevil:
The vine weevil is about ten millimeters long and black in color. They travel in the dark looking for food. An evergreen olive tree is just the thing. You can recognize the infestation by the following symptoms:
- adult beetles leave marks on the leaves
- the white dot in the root area could be a cluster of eggs
- Deficiency symptoms cause drooping shoots and leaves
The control of the vine weevil is possible with environmentally friendly methods. While the adult beetle is black, it is primarily the white dot, the larva, that can damage the tree. Nematodes help against this. These are roundworms that prey on the larvae.
Wood wool can also help against the parasite. A bucket filled with it will attract the vine weevil. You can recognize the success by the fact that the wood shavings are becoming increasingly black because the beetle has colonized them.
meadowfoam cicada
The meadowfoam planthopper has only been a feared pest on olive trees for a few years. While one or the other white spot is still harmless, a heavy infestation can lead to clear symptoms. In particular, the transmission of the fire bacterium is a feared complication of the meadowfoam planthopper.
The following symptoms indicate the pests:
- adult insects are clearly visible. They are dark brown to black in color and elongated in shape
- white coating and pustules indicate the infestation
- Treatment is possible with sticky traps, as the females cannot then lay eggs
- You can finally remove white deposits with the shower